Electromagnetic coil.



E. Hf GOLPITTS. ELBGTBOMAGNBTIG COIL. APPLICATION FILED MAR.25, 1909.

' Patented Nw. 3, 2.914,

2 SgEETS-SHEET 2.'.

E. H.'c0LPITTs. ELBGfIROMAGNETIG COIL. APPLIGATIOI?v AFILED MAR. 25.,19,09-

nl A

//7 Ven for Vw/'f7 /vf 6040/775. by

' siding at Elizabeth, in the'county of Essex.

' the difficulty of securing a -tensity UNITEp sTATEsgrATENT oEEIcE.

EDWIN n. conrrr'rs, or ELIZABETH, NEW JERSEY, nssIeNOE To wEsTEnNELECTRIC COMPANY, or CHICAGO, ILLINOIS, a CORPORATION or ItLrNoIs.

-ELEC'IEOMAGNETIG COIL.

T0 all/whom it magy concern.'

B e it known that 1 EDWIN H. CoLrITrs, a subject of the lKing .of GreatBritain, re-

and State of New Jersey, have invented a certain new and usefulImprovement in Electromagnetic Coils, of which the following is a full,clear, concise, and exact description.

|Tl1is`invention relates to electromagnetic coils, and its principalobject is to provide an efficient coil whose windings are eX- trenielyaccurately balanced with substantially nomutual inductance betweenthemf' As is well known, it. is a common practice to use-portions of twogrounded telegraph lines as the sides of a metallic telephone circuit.In general this involves' the insertion Aof inductive coils in theVtelegraph line, and in branches leading therefrom to earth, '1n a mannerwell understood by thosev skilled in the art. vPrior to my invention,however,y four. coils have been used at each telephone stationVeach coilconsisting of. al

separate unit comprising a core carrying 'two serially connectedwindings, one such coil being inserted serially 'in each telegraph line,'and one in each of two grounded branches from said lines. This practicehas proved unsatisfactory by. reason of the number of coils required,the space occupied 7 thereby, the disturbances produced in said coils'by currents traversing adjacent coils,

' balanced condition of thel telephone circuit due to vcoinmercialvariations in the impedance of coils, and the difficulty of preservingthe balance of' said circuit when once established due to thevariationsl in, the impedanceI of txe coils attending changes inininvention a coil is provided`.wliich is free `from thesevobjections.;A

4The above and otheri objects of this in.- vention will be fully setforth in the following specification and claims, and will be morereadily understoodby reference to the accompanying drawings, in which-Figure l is a vertical sectional view of the coil of my inventionremoved from .the case, Fig. 2 is a top view, partly 1n section,- ofsaid coil; g3 is a side elevation, partly in section, ofisaid coilmounted Ona base;

4$pecificaton of Letters Patent.

the

of the telegraph currents. By my Patented Nev. s, 1914;

mutation mea Marcil 1909.- s'enai No. 485,690.

and llig. l is a circuit' diagram showng'a mode of connectionof the coilina composite telephone and telegraph system.

The preferred embodiment o my invention consists of a coil comprisingtwo pairs or groups of windings upon aci'rcular or toroidal iron core;the'windings of each pair being" connected serially anddiiferentiallyand placed, preferably, in diametrically oppositepositions upon said'core, and

a covering of iron wire laid upon either the peripheral or end surfaces,or upon both said surfaces, concentrically with the axis' of the core.VW'ith thist construction the flux ofthe opposing magnetic fields,established by -currents passing through the diflferentially connectedwindings in series, isA

forced to traverse the air between the core and the .outer wire coveringor return path, as a result of which,`by virtue of the redoininance ofthe airrcluctance over th t of the iron, the impedance of the windings'is 'rendered practically constant, as will be readily understood Iby'those versed in the electrica-l art. The -iron wire covering,

therefore, vforms a part of the effective magnetic circuit of eachwinding. Furthermore, the outer iron wire not only serves to preventvthe flux fromvstraying intothe field oftadjacent apparatus, in which, itmight develop disturbances, but renders it possible to .cover orlincl'ose the structure with a metal case 'without encoiuitering thetransmission losses which would otherwise result from 4excessiveeffective resistance caused .by the developmentof eddy currents in thesolid metal of said case. .The structure just described may, thereforabeused wherever .itsfea'tures have .a field, particularly in compositecircuits, with, distinctly improved results.. f

ln accordance with-anotherfeature of this inyention,ltwo setsl'ofwindings are placed upon a ring core and so arranged with relationtofeach other that the polar direction of the magnetic lines induced byone set of windingsv is substantially at right angles to that induced bythe other; More specifically these windings may be in tw'opairs upon atoroidal iron core, each pair comprising `two or -diametricallyopposite, wind- I alternate, u inffs connected serially andldifferentially. ith this construction it is found that if the pairs ofwindings be substituted for the pair of coils used heretofore, in eitherthe telegraph lines or in the grounded branches therefrom, the result isa distinct and uniform improvement in operation. This improvementresults from the high degree of balance which maybe attained as a resultof the use of a core commonto both pairs, whereby the unbalancing effectof structural variations is reduced to a minimum; in the constancy ofbalance resulting from the predominance of the reluctance of the airpath over that of the iron; and in the absence of internal mutualinductive disturbances, or so called cross tire which disturbances areeliminated by the differential relation which the pairs bear to eachother. The coil as just described may be embodied in composite 'circuitswith improved results, where space permits' of proper separation of thecoils, and by virtue of its eXtreme simplicity and its capability ofreplacing two coils of the v pior art, is an economical form to use.

here, however,'it is desirable to mount the coils adjacent one another,it is preferable to provide against cross talk, cross signaling and eddycurrent losses by covering either the peripheral or end surfaces, orboth said surfaces, with iron wire, as in the case of the firststructure described.

Referring to Figs. 1 and 2, showing a coil constructed in accordancewith the preferred form of my invention and 'provided with fourwindings, 5 is a circular or toroidal core of iron wire wrapped orotherwise covered with suitable insulating material 6.

Plates or separators 7 of insulating material are placed upon the coreat proper intervals, as, for example, in the structure shown, atintervals of ninety degrees, between which separators the windings 8, 9,10 and 1l are `ilaced, lsaid windings being wrapped or otherwise coveredwith suitable insulating material 12'. Upon the peripheral surface ofthe'structure just described, and preferably also uponthe ends, ironwire13 may be laid concentrically with the axis of the core, said wire beingheld in position bysome suitable means, as, for example, the cords 14.The alternate, or 'in the structure shown, the vdiametrically oppositelwindings 8 and 9, 1Q and 11, are-connected serially and differentiallyand may conveniently be thus Joined in the central opening of the core.

Referring to Fig. 3 the coil as, describedabove is placed in an ironcase or cover 15 and the vacant space filled with some suitableinsulating compound 16v preferably an `insulating compound adapted toexcludeair,

as, forexample, a composition of resin and resin oil. The structure thusincased may 'then be mounted'with theopen end downward upon a base 17secured thereto by screws 18,' passing through ears 19. The free 65fendsof the 'two pairs. of windings may-be led out through openings inthe base and in slots 20, 21, 22 and 23, to terminals 24, 25,

form of my invention in a composite tele.

phone and telegraph circuit, 28 and 29 are portions of groundedtelegraph linesleading from telegraph stations 30 and 31, over@ whichportions it will be assumed that telephone transmission from telephonestation 32 is desired. As shown inthe diagram, a coil 33 of my inventionis directly connected with the telegraph lines, one pair ofdifferentially connected windings, 8 and 9, being inserted serially inthe telegraph line 28 from station 30, the other pair of differentiallyconnected windings, l0 and 11, being inserted serially in thetelegraphline 29 from station 31. 34 and 35 are condensers comiected asusual in grounded branches from the telegraph lines. The telephone setis bridged across the telegraph lines 28l and 29, the usualcondensers'36 and 37 being connected in series therewith. Connected'withthe bridged telephone branch are two grounded branches 38 and 39 leadingfrom each sideof the telephone set, said branches including,respectively, the usual condensers 40 and 4l, and the differentiallyconnected windings-8 and 9 and 10 and 11, of the c oil 42, also of myinvention. 43 and 44 are telegraph keys and 45 and 46 'are sources oftelegraph currentl .v

Incomposite systems of the general type described, equipped with coilsconstructed in accordance j withl the preferred form of my invention,the lparts of said coils being dimensioned in accordance with well knownelectrical laws,'it is found that telephone currents are practicallyconfined to the metallic circuit comprising portions 28 and 29 and thetelephone branches connected'thereto, since in any of the four paths toearth at each station, a pair of windings is included,

which windings, although differentially connected, possess suiiicientvinductance to properly o pose the passage of telephone currents.[oreover, by virtue of the use of iron wire, lsuch passage to earth oftelephone currents as may occur is not attendedwithl #excessivedevelopment of eddy currents and lio consequent energy losses, by reasonofthe" low degree of effective resistance which' the pairs of windingspossess. Also, since 'in 'eahh coil the windings 'are .upon the samecore, coils ofthis type may readily be manufactured in `which theimpedances of the pairs of windings -areequal, which, as alreadyindicated, isesse'ntial to a balanced condition of the telephonecircuit. v'Furthermore, since theflux ofthe opposing magnetic fields,which the telegraph currents establish, traverses a section of airbevfore reaching the outer Wireor'mhlin 'Lp-ath, the desired constancy ofimpedance and conse uentpreservation of balance are cured. inc e thewindings 8 and 9 setup epljactically equal eld of force at right anglesto that set up by 10 and 11, current -flow in the telegraph circuits dueto mutual induction, or cross re prevented. v

, Having described my mventlon, I clalm:

as it is'lmown, is

1. A toroidal coil comprisingfa core, a.

plurality of windings consecutively arranged about said core, and meansinterconnectingand means for interconnecting non-adjacent ,v

coilsv differentially in series.

3. 3A coil comprising a toroidal' co5" plurality of windings thereonarrang mutua-ll non-inductive grou sa'nd a cov-5.

ering o magnetic material orming :sp-art, of the1 ee'ctive magneticclrcult o eachV v winding.

In witness whereoL-I, hereunto subscribe my name tliis 24th day ofMarch, A. D., 1909. l

Witnessesi', I y

IRVING MACDONALD,I RALPH G. JOHANSEN.

'EDwINfH o o'LPIlT-Ts. f

